Chiefs RB Jamaal Charles has lost two fumbles in four games this season, matching his total from the 2010 season.

A handful of observations as we turn the page on Week 4 and head into Week 5:

» The fumbling epidemic. Ryan Mathews, the San Diego Chargers' 2010 first-round draft pick, did not start last Sunday because of a fumble in Week 3. BenJarvus Green-Ellis of the Cincinnati Bengals had never lost a fumble in his entire NFL career -- a span of 589 touches -- but now has lost one fumble in each of the past two weeks. Jamaal Charles, the league's second-leading rusher with 415 yards, fumbled twice in Week 4 in what could have been critical possessions in a comeback attempt against the Chargers.

Fumbling as a whole is up so far this season for running backs. There has been one fumble lost every 100.3 rushes in 2012; over the past five seasons, there was one fumble lost every 118.6 rushes.

When a running back fumbles, it really stirs me up. Their job is to hold onto the ball. Fumbling, especially from a running back, is unacceptable.

» Drops killing Detroit. If one thing upsets me more than fumbles, it is probably drops. Heading into Week 4, the Lions led the league in drops. On cue, Brandon Pettigrew dropped what could have been the game-changing touchdown in Detroit's loss the Vikings. He was wide open in the end zone, ball hit him right in the hands, drop. That is very frustrating for a quarterback who stands tall in the pocket, takes a hit from a pass rusher but still throws a perfect strike to the end zone. How do you expect Matthew Stafford to find a rhythm when his receivers can't even catch the ball -- and that includes Calvin Johnson, who was guilty of at least one other drop on Sunday.

» The Jets' real problem. You can talk about replacing Mark Sanchez with Tim Tebow all you want, but that only serves to distract from New York's real problem: defense. Led by the overly expressive mouths of Rex Ryan and Bart Scott, the Jets used to hit you in the mouth and then tell you just how great they were; now, they can't even tackle. They are giving up 173 yards on the ground per game, second worst in the league. They can't get any pressure on opposing quarterback without blitzing, and even then it is still questionable. So talk all you want about Tebow, but he isn't going to solve this problem.

» Can't hold the ball forever, fellas. Too often, the offensive line and running back get blamed for protection issues, but the quarterback needs to take some responsibility as well. In Week 3, we saw Michael Vick get blitzed on the goal line and not get rid of the ball fast enough, resulting in a brutal hit and a long fumble return for a touchdown. In Week 4, Jake Locker was knocked out of the game (and perhaps longer) not because of a missed block, but because he didn't get rid of the ball when the defense sent more than his team could block. Vick and Locker need to see the defense and react quickly. I put both of those on the quarterback.

» Houston is well-rounded. The Texans' top-ranked scoring defense is getting much of the credit for the team's hot start, and rightfully so, but this team is loaded on offense, as well. The Texans have ability to win the old-fashioned way: run the ball and play great defense. With Arian Foster and Ben Tate in the backfield, they are controlling the game and still getting explosive plays. So yes, the defense is only giving up 14 points per game, but the offense is also putting up 31.5 per game. There is plenty of room for error when you have a 17.5-point scoring differential.

Harrison: Week 5 Power Rankings

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» The surprising Vikings. After starting with little hope, I have been pleasantly surprised by Minnesota's skill players. Jerome Simpson's return from suspension gives the Vikings speed to complement Percy Harvin, and his impact was felt almost immediately. Not only did Simpson finish the game with four receptions for 50 yards, but he also drew two defensive pass interference calls on deep plays down the sideline. His speed will allow Harvin more room underneath for short throws, which Harvin can turn into long gains with his yards-after-catch ability.

» The real Wildcat.San Francisco 49ers backup Colin Kaepernick looked impressive Sunday. He runs the Wildcat better than anyone I've seen, similar to how Brad Smith was used in New York before departing for Buffalo. And before you say it, Kaepernick is faster than Tebow and throws it better. This new wrinkle to the 49ers might be a big part of the game plan for the rest of the year. If used properly, it will give opposing defenses one more thing to worry about it, resulting in more vanilla defensive looks for Alex Smith.